The homeowner, George Wray, was severely burned Friday when he opened the package, which had been left atop the steps of his duplex on 222nd Street in the Brookville neighborhood, and the police were continuing to search on Wednesday for whoever sent it. The police said they did not believe the package was intended for Mr. Wray.

“We will not know motive until we have a target,” Robert K. Boyce, the chief of detectives, said at a news conference on Tuesday.

Mr. Wray, 73, sustained second-degree burns over 80 percent of his body when the package, a foot-long cardboard tube containing flash powder, blew up, the police said. Flash powder is a low-grade explosive commonly used in stage productions like plays and concerts.